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|THE EDITORIAL DEBATE: PROS AND CONS
|Year : 2016 | Volume
| Issue : 1 | Page : 25-26
Epidermal growth factor gene amplification in high grade gliomas
Department of Pathology, Christian Medical College, Vellore, Tamil Nadu, India
|Date of Web Publication||11-Jan-2016|
Department of Pathology, Christian Medical College, Vellore, Tamil Nadu
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Chacko G. Epidermal growth factor gene amplification in high grade gliomas. Neurol India 2016;64:25-6
The past decade has seen much progress in our understanding of the molecular pathology of gliomas.
Isocitrate dehydrogenase (IDH) 1 and 2 mutations are now recognized to discriminate biological classes of diffuse gliomas. Gliomas with IDH mutations are associated with a better prognosis., Among the IDH mutant gliomas, 30–40% demonstrate 1p/19q codeletions; of the remaining, 94% exhibit tumor protein p53 (TP53) and alpha thalassemia/mental retardation syndrome X-linked (ATRX) mutations. These alterations are increasingly accepted as defining oligodendrogliomas and astrocytomas, respectively. Among the glioblastomas (GBMs), most primary GBMs are IDH wild-type and most secondary GBMs are IDH mutated ones. Primary GBMs show additional molecular alterations in the tyrosine kinase receptor (TKR), retinoblastoma 1, and p53 families. In the TKR family, epidermal growth factor receptor (EGFR) amplification, phosphatase and tensin homolog deletion, and mutations of phosphatidylinositol-3-kinase are common. In contrast, secondary GBMs show a high frequency of IDH and TP53 mutations and ATRX inactivation.
EGFR is a transmembrane glycoprotein that becomes autophosphorylated once it binds to its ligand. This induces subsequent activation of the signaling pathways involved in regulation of cell proliferation, differentiation, and survival. Approximately 40–50% of GBMs show amplification of EGFR and about half of these have variant III mutation. This mutation causes truncation of the receptor and leads to tyrosine kinase activity. There are controversial results on the prognostic relevance of EGFR amplification.,,,,,
In a study published in this issue of Neurology India, a large series of high-grade gliomas have been studied using fluorescence in situ hybridization to assess the frequency of EGFR amplification. The authors found EGFR amplification in 34% of adult GBMs.
The term GBM with an oligodendroglial component (GBM-O) has been used in the WHO 2007 classification for GBMs with areas similar to that seen in anaplastic oligodendrogliomas. It is, however, increasingly accepted that if these tumors exhibit 1p/19q codeletion, they are in fact anaplastic oligodendrogliomas., The current study found the frequency of EGFR amplification to be similar in those defined as GBM, and those that were diagnosed as GBM-O. None of the patients with GBM-O in their series had 1p/19q codeletion. Therefore, by the current thinking, these too were in fact GBMs, and this explains the similarity in the frequency of EGFR amplification in the two groups.
Recently, TERT promoter mutations have also been found to be key molecular determinants of biologic behavior in gliomas., In a study published by The Cancer Genome Atlas More Details, among WHO Grades II and III diffuse gliomas, 96% of cases with IDH mutation and 1p/19q codeletion showed TERT mutations while only 4% of IDH mutant gliomas without 1p/19q codeletion showed the mutation. Simon et al., found TERT mutations more often in primary than secondary GBMS. They also reported an inverse correlation between IDH1/2 mutations and TERT promoter mutations.
Although the diagnosis of gliomas so far was based primarily on the histological features, these recent developments have forced a relook at the classification of gliomas. As the number of clinically-relevant genetic alterations increase, there will most certainly be a transition toward the development of a molecular diagnostic panel for gliomas. In fact, the “integrated diagnosis” approach mooted by the International Society of Neuropathology-Haarlem Consensus Guidelines recommend the incorporation of molecular data as part of the layered format of reporting for gliomas.
While there is no doubt that this approach which integrates molecular data with the histological picture is of utmost relevance to clinical treatment and outcome, the challenge we face in India is to be able to apply these norms uniformly at all centers of care. Perhaps centralized facilities that offer these services at a subsidized rate are the need of the hour.
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